[Closed] Recommend me a single speed tensioner for an unusual purpose

I'm trying to sort out the tensioner on the Trivelox three speed gears on a vintage tandem.
It's an odd system where the chain stays in line and the sprockets move across the hub on splines.
The tensioner part was missing when I bought it. it had been bodged with an old Simplex derailleur, but didn't work.
I've now bodged it with a Rohloff tensioner, which probably would work, except that the cage sides are too close together for the 1/2" x 1/8" chain that it needs for the thicker chainring and sprockets.

Is there a single speed tensioner around that looks anything like this ?

[img] [/img]

[img] [/img]

As you can see, there are at least two different types. I'm not sure which I want.
Does anyone make a tensioner that looks close to either of those and, most importantly, will take a 1/8" chain ?